In addition to protecting bacteria from lysis, the peptidoglycan cell wall plays an important, underappreciated role in several physiological processes. These range from the basic biological functions of creating cellular polarity, influencing differentiation and impeding virus entry, to contributing to host attachment, toxin production and recognition by the innate immune response. Even less well understood are the contributions of bacterial morphology to nutrient accumulation, attachment, motility, chromosome segregation, predation, biofilm formation and virulence. Our long-term goal is to understand the structure, synthesis, regulation and functional implications of peptidoglycan and the enzymes that create and modify it. In particular, we've been searching for the physiological functions of the low molecular weight penicillin binding proteins, a large family of peptidoglycan-modifying enzymes that are present in multiple forms and highly conserved across the bacterial kingdom. These enzymes interact with the bacterial division protein, FtsZ, to create cells of defined and uniform shape via reactions that are either independent of or which precede the now-classic division pathway initiated by FtsZ. Of great import is that newly described phenotypes in multiply-mutated strains allow questions of cell shape and polarity to be approached by genetic techniques not previously available for such studies. We propose to refine and characterize the functioning of this "morphological pathway" by pursuing the following specific aims: 1) characterize the role of FtsZ in generating and localizing inert peptidoglycan; 2) characterize the roles of peptidoglycan hydrolases in cell shape and integrity; 3) define how interacting helical structures propel growth of the wall and envelope; and 4) isolate and characterize suppressor mutants to define the morphological pathway in more detail. These goals will be realized by creating strains deficient in portions of the proposed pathway, by assaying current FtsZ mutants and creating new ones, and by isolating suppressor mutants to define additional components of the pathway. [unreadable] [unreadable]